Effect of hybridization of fibers on the properties of high volume fly ash concrete and its numerical simulation

High volume fly ash (HVFA) is used as cement substitute in many cementitious materials. In recent years, hybrid fibers such as steel and polypropylene have been added to improve the mechanical characteristics. The usage of three fibers combinations is relatively a new concept in HVFA concrete. In this thesis, natural basalt fiber has been combined with steel and polypropylene due to its availability and low cost. Due to the concern about chemical resistance, chemical durability and performance of silane coated modified and non-modified basalt fibers are studied. The fibers were immersed into twelve solutions for 62 days considering the concrete medium. The failure pattern and damage features of the fibers were sorted with the observation of surface by scanning electron microscope (SEM) and their compositions were identified using energy dispersive X-ray spectroscopy (EDX). Long term mass retention capacity was also summarized. The result revealed that the modified fiber exhibits superior properties compared to the non-modified fibers based on morphological and chemical analysis of basalt fibers. Post this analysis; varied hybrid fiber combinations (both two types and three types) were tested on cement mortar specimens to identify the optimal fiber percentages. Based on the experimental results, equations and artificial neural network were developed to predict the compressive and flexural strength. Two optimum hybrid fiber percentages were found out from the overall analysis of compressive and flexural properties i.e., 1.5% steel, 0.5% polypropylene (1.5S0.5P) and 1.0% steel, 0.5% polypropylene, 0.5% basalt (1.S0.5P0.5B). Optimal percentages were then used to test concrete specimens. Pre and post cracking mechanical tests of the concrete were carried out. The result of the compressive strengths of three types of hybrid fiber concrete showed appreciable increase by 5.44% and the splitting tensile strength increase was 6.77% in comparison with two type hybrid. Detailed durability properties of optimum hybrid fiber HVFA concrete were conducted along with advanced computed tomography X-ray scans to investigate the durability characteristics of HVFA hybrid fiber concrete. These techniques together confirmed the reduction in porosity and hence the durability of concrete directly suggesting the benefit of the added silane coated basalt fiber. Numerical models were validated using experimental results for the use of three different fibers in concrete. The model was prepared considering the separate geometry and random orientation of individual fibers. Nonlinear analysis was performed under static load to investigate their failure modes in terms of ultimate load. This model will provide a guideline for the optimum use of three different fibers

The Impedance of a Loop Near a Conducting Half-Space

The change in complex impedance between an ideal one-turn circular coil located above and parallel to a conducting half-space with respect to a similar isolated coil has been calculated. From this result a series expansion of the integrand allows the solution to be approximated by terms expressed as complete elliptic integrals. Results have been calculated for the change in impedance as a function of the lift-off distance and the conductivity of the half-space for a coil of representative.radius

Numerical Characterisation of Supersonic Exhaust Diffusers

Rocket motors that are designed to operate at high altitudes need a nozzle with a large expansion ratio to maximize the thrust at much lower atmospheric pressure than that of the sea level pressure. Accurate performance of these nozzles cannot be obtained when static tested on ground. Computational fluid dynamics (CFD) analyses have been performed to characterise the supersonic exhaust diffuser (SED). The results obtained from the CFD analyses have been found to be in good agreement with experimental and numerical values reported in the published literature. Started and un-started regions of the SED have been identified with the CFD results

Determinants of male participation in reproductive healthcare services: a cross-sectional study

Background The role of male’s participation in reproductive healthcare is now well-recognized. The present study investigated the role of men in some selected reproductive health issues, characterizing their involvement, including factors influencing their participation in reproductive healthcare services. Methods This study was conducted in the working areas of urban and rural implemented by NGOs. The sample-size was determined scientifically. The systematic sampling procedure was used for selecting the sample. The study included 615 men aged 25-45 years. Bivariate analysis was performed between male’s involvement as the dependent variable with several independent variables. Logistic regression analysis was applied to assess the effects of risk factors on the participation of men in reproductive health care services. Results The mean age of the respondents was little over 34 years while their mean years of schooling was 3.7, and their mean monthly income was about Tk 3,400 (US$ 1 = Tk 70) at the time of the study. Rickshaw-pulling and driving was the main occupation of the respondents from the urban while farming were main occupation in the rural area respectively. About two-thirds of the respondents discussed reproductive health issues with their wives and accompanied them to healthcare facilities. The current contraceptive-use rate was 63% among the men who attended the evening clinics. Results of bivariate analysis showed a significant association with education, occupation, income, access to media, and number of living children. Results of logistic regression analysis showed that secondary to higher education level, number of living children, paid employment status, long marital duration, and access to media were important correlates of males’ involvement in reproductive healthcare services. Conclusions The results imply that a greater integration of reproductive healthcare matters with the Millennium Development Goals and increasing perception of men through enrollment in various components of reproductive activities will produce synergistic effects

Experimental Demonstration of Microwave Signal/Electric Thruster Plasma Interaction Effects

An experiment was designed and conducted in the Electric Propulsion Laboratory of NASA Lewis Research Center to assess the impact of ion thruster exhaust plasma plume on electromagnetic signal propagation. A microwave transmission experiment was set up inside the propulsion test bed using a pair of broadband horn antennas and a 30 cm 2.3 kW ion thruster. Frequency of signal propagation covered from 6.5 to 18 GHz range. The stainless steel test bed when enclosed can be depressurized to simulate a near vacuum environment. A pulsed CW system with gating hardware was utilized to eliminate multiple chamber reflections from the test signal. Microwave signal was transmitted and received between the two hours when the thruster was operating at a given power level in such a way that the signal propagation path crossed directly through the plume volume. Signal attenuation and phase shift due to the plume was measured for the entire frequency band. Results for this worst case configuration simulation indicate that the effects of the ion thruster plume on microwave signals is a negligible attenuation (within 0.15 dB) and a small phase shift (within 8 deg.). This paper describes the detailed experiment and presents some of the results

Forecasting Volatility of Dhaka Stock Exchange: Linear Vs Non-linear Models

Prior information about a financial market is very essential for investor to invest money on parches share from the stock market which can strengthen the economy. The study examines the relative ability of various models to forecast daily stock indexes future volatility. The forecasting models that employed from simple to relatively complex ARCH-class models. It is found that among linear models of stock indexes volatility, the moving average model ranks first using root mean square error, mean absolute percent error, Theil-U and Linex loss function criteria. We also examine five nonlinear models. These models are ARCH, GARCH, EGARCH, TGARCH and restricted GARCH models. We find that nonlinear models failed to dominate linear models utilizing different error measurement criteria and moving average model appears to be the best. Then we forecast the next two months future stock index price volatility by the best (moving average) model

Comparative Analysis of Downlink Packet Scheduling Algorithms in 3GPP LTE Networks

Long Term Evolution (LTE) mobile network aims to support high speed network services even in highmobility scenarios. To achieve this goal, LTE adopts some advanced features in Radio Resource Management (RRM) procedures. Among them, LTE packet scheduling plays a fundamental role in maximising system performance. In this paper, a comparative analysis on the performances of Proportional Fair (PF), Exponential/Proportional Fair (EXP/PF), Exponential (EXP) Rule, MaximumLargest Weighted Delay First (M-LWDF), Logarithmic (LOG) Rule and Frame Level Scheduler (FLS) LTE downlink packet scheduling algorithms is reported. Performance is evaluated in single cell with interference environment while increasing user number and user speed. Results show that for multimedia flow, FLS scheme outperforms other five schemes in terms of packet delay, packet loss ratio, and average throughput, whereas for best-effort flow, EXP-PF scheme shows better average throughput performance on average as compared with other algorithms being considered herein

Whipple's pancreaticoduodenectomy: perioperative outcomes in a tertiary care hospital in Dhaka, Bangladesh

Background: Pancreaticoduodenectomy is one of the most complex surgery with significant mortality and morbidity. Though the mortality rate has steadily improved, morbidity continues to be high. The aim of this study was to demonstrate the perioperative outcome following this procedure at our hospital.Methods: This retrospective study was conducted in the department of Surgery, Sir Salimullah medical college and Mitford hospital from July 2018 to December 2019. A total of 29 patients who undergone pancreaticoduodenectomy were included in the study. Preoperative, intra-operative and post-operative data were analyzed with emphasis on the morbidity and mortality rates. None of the operated patients received any types of neoadjuvant therapy.Results: Out of 29 patients who underwent PD, 18 (62.1%) were male and 11 (37.9%) were female with a median age of 53.7 years. The most common (34.5%) age group of the patients were 51-60 years. Jaundice was the commonest (89.7%) presenting symptoms followed by anorexia (75.9%) and abdominal pain (48.3%). Overall complications occurred in 37.9% patients, including wound infections (31.0%) and post-operative pancreatic fistula (6.9%). The post-operative mortality rate was 6.9%.Conclusions: PD still causes considerable morbidity and mortality. With careful patient selection, adequate preoperative preparation, surgical technique, excellent critical care management PD can be performed safely. At our center we have a reasonable volume and our data are comparable to literature data.

Baseline antenna design for space exploration initiative

A key element of the future NASA Space Exploration Initiative (SEI) mission is the lunar and Mars telecommunication system. This system will provide voice, image, and data transmission to monitor unmanned missions to conduct experiments, and to provide radiometric data for navigation. In the later half of 1991, a study was conducted on antennas for the Mars Exploration Communication. Six antenna configurations were examined: three reflector and three phased array. The conclusion was that due to wide-angle scan requirement, and multiple simultaneous tracking beams, phased arrays are more suitable. For most part, this report studies phased array antenna designs for two different applications for Space Exploration Initiative. It also studies one design for a tri-reflector type antenna. These antennas will be based on a Mars orbiting satellite